With an increased number of smartphones in cellular communication networks, mobile network operators are confronted with various challenges. One challenge relates to how to provide an always-on-line experience for a very large number of smartphones, or in fact any type of user equipment.
As mentioned, the smartphone usage requires always-on-line experience for end users similar to PC-type programs. The always-on experience implies short reaction time for data arrival and data transmission. Therefore, one way to obtain this would be to maintain all smartphone users in RRC_CONNECTED state. The RRC_CONNECTED state is known from Third Generation Partnership Project (3GPP) terminology and relates to Long Term Evolution (LTE) systems. However, maintaining all smartphones in RRC_CONNECTED state may suffer from disadvantages such as that the smartphones would consume most periodic resources on Physical Uplink Control Channel (PUCCH). The number of smartphones may be very large, for example up to 65 536 smartphones as allowed by the Cell-Radio Network Temporary Identifier (C-RNTI) having 16 bits. With such large number of smartphones, the periodic resources on PUCCH will not suffice. However, most of the periodic resources are actually not used, because the always-on traffic only create chatty-like small packet in most of the time, e.g., background traffic, but not always continuous traffic flow, e.g., FTP traffic. A scenario like this is referred to as enhancement for Diverse Data Applications (eDDA) within 3GPP.
As an example, the periodic resources on PUCCH are consumed by a channel Quality Indicator (CQI) in a known LTE system. The CQI is reported periodically as configured by a base station. The CQI is for example used as input to channel adaptation in the base station. Channel adaptation relates to how for example modulation and coding schemes (MCS) are set in relation to quality of a channel.
A user equipment (UE) can be configured by Radio Resource Control (RRC) signalling to transmit CQI periodically on a specific PUCCH resource. The specific PUCCH resource has been configured by RRC signalling.
Back to the eDDA scenario, a problem is how to obtain CQI information in an efficient and flexible manner.
On one hand, if periodic CQI is enabled, the consumed amount of PUCCH resources would be large. Since most of the CQI information is not actually used, a disadvantage is that the CQI information often is unnecessary.
On the other hand, if periodic CQI is disabled, the downlink data flow can only use conservative modulation and coding schemes or re-transmission to match a desired transmission performance, since not enough CQI information is available to the base station.
In order to overcome this problem, a-periodic CQI reporting is also defined for 3GPP LTE systems. Specifically, a bit in an uplink grant may trigger a user equipment to transmit a channel quality report on a Physical Uplink Shared Channel (PUSCH). The channel quality report may be transmitted together with a data transmission or without a data transmission on PUSCH. A-periodic reporting of CQI is controlled by the base station, such as an eNodeB. In this manner, the CQI reports are sent when the uplink grant indicates that the user equipment shall send CQI information on PUSCH.
In order to save periodic CQI resources on PUCCH when a-periodic CQI on PUSCH is activated, a proposal suggests that the periodic CQI transmission is prohibited when a-periodic CQI on PUSCH is activated. Specifically, the transmission of periodic CQI report is cancelled during a predetermined time, when the user equipment has received a request for CQI on PUSCH from the base station. Thus, the user equipment makes sure that no periodic CQI is sent on PUCCH during the predetermined time if an uplink grant indicates that the user equipment shall send CQI information on PUSCH.
From the above, the CQI reporting mechanism can be said to be divided into two types, i.e. periodic CQI on PUCCH and a-periodic PUSCH.
Under the scenario of eDDA, as is analyzed above, periodic CQI on PUCCH is not resource efficient enough to support the large number of always-on traffic, which occurs due to the usage of smartphones.
A-periodic CQI on PUSCH has disadvantages as well. Specifically, CQI information has to be sent by UE every time there is downlink data arrival at the user equipment. This is efficient when there is uplink data to be sent on PUSCH together with the CQI information to the base station. However, when there is no uplink data transmission, i.e., uni-directional downlink traffic, one uplink resource block containing only CQI information is not resource efficient.